Sheet abrasive



Patented June 15, 1943 SHEET ABRASIVE Robert W. Hackett, East Braintree, Mass, assignor to Abrasive Products, Inc., South Braintrec, Mass, a corporation of Massachusetts No Drawing. Application September 22, 1941,

Serial No. 411,850

7 Claims. (01. 51-595) This invention relates to the manufacture of flexible sheet abrasive materials.

Essentially, the invention provides a treatment of a flexible sheet backing material, which permits the use of cheaper stock without detrimentin fact with improvement-to the characteristics required in the production of a satisfactory flexible abrasive sheet product.

Additionally, however, the treatment results in the production of a backing material having wide versatility from the standpoint of adhesive receptivity, thus permitting a for subsequent coatings, which are to act either as the grit bonding adhesive or as a protective back coating or coatings.

In its most important application, the invention relates to abrasive materials which are required to possess qualities of high pliability, softness and conformability, for use as so-called finishing papers, but wherein toughness and strength are equally important attributes. The sheet materials herein described may be cheaply fabricated insofar as both ingredients and operations are concerned, and without necessitating an unsatisfactory compromise between strength and pliability. Though I use a cheaper sheet material, usually a paper, the treated paper is at least equal to, if not superior, in strength to a rope kraft paper, and the preparation technique is far simpler than any technique heretofore suggested for adapting such cheap papers for satisfactory commercial use in the fabrication of finishing papers, especially because the treatment may be performed, in the case of paper, without any necessary resort to the relatively complicated precautionary measures heretofore'required to prevent appearance-marring, as well as quality reducing, crinkling of the paper during spreading of the aqueous coatings, and particularly during spreading of the initial sizing coat.

As an example of a product fabricated in accordancewith this invention, the following may be described.

As a backing material I have successfully used 40# Duracel, which is a product readily available on the market, and is a'paper having an alpha cellulose content exceeding 90%. I coat this material with a solution of diethylene glycol diabietate in a penetrating volatile hydrocarbon solvent, as xylene or toluene, by doctor spreading, or by dipping the stock in the solution at room temperature. Preferably this operation is a continuous operation, and as the stock passes beyond the solution-applying apparatus, the excess is squeezed off, as by pressure rollers, and the stock choice of materials I is allowed to dry. I haveiound that the dryin can be accomplished at normal room temperature, in approximately one half hour. My experience has shown that hot calen'dering or tentering of the stock during or after coating is entirely unnecessary, as the applied material will dry without causing non-uniform shrinkage or crinkling in the stock. This is in marked contrast to aqueous paper sizing treatments, which require hot calendering operations to counter the natural tendency of water to cause uneven drying and,

shrinkage in paper stock, and require long drying periods and/or elevated temperatures and/or controlled conditions of humidity 'to produce satisfactory results. By the use of my particular coating material, such controls may be obviated. and the coating operation is greatly simplified and cheapened. The simplification, in turn, improves the uniformity of the product by reducing the variables involved in the coating operation.

Moreover, I have found that such a stock, so coated, has, after drying, qualities of toughness and strength equivalent to those found in rope kraft paper, with the diethylene glycol diabietate unifying and bonding the paper. The coating dries evenly, so that the stock presents a uniform, evenly filled, smooth finished surface, of a type particularly desirable for receiving subsequent coats. At the same time, the diethylene glycol diabietate, even though-unmodified, does not detract noticeably from the softness, pliability and limpness of the paper stock.

After completion of the above treatment, the coated heet may receive a coating of an adhesive for attaching abrasive-grit thereto, and herein lies an important feature of the invention, in that V I'have discoveredthat such a coated sheet will receive a coating of conventional glue adhesive, hot aqueous spread, with remarkable qualities of adhesion and bond, considering the non-watersoluble nature of the initial diethylene glycol diabietate coat. Such success is undoubtedly due to some property of diethylene glycol diabietate which renders it water-wettable, and, to some extent at least, miscible with glue, despite its general non-water-soluble characteristic. It is probable that the alkalinity of conventional glue .adhesives is also partially responsible for the success.

Thus I have "been enabled to prepares finishing paper, as above described, which has a conventional glue making coat, conventional grit, and a novel bond thereof to a backing by reason or its application over a priming, sizing, or impregnating coat of a. substance which, while being compatible with the glue and water-wettable for the purposes of an aqueous application v without danger of crinkling as a result of the water contact, additionally is of such a nature that it imparts water resistance as well as toughness and strength, to the backing itself.

The water resistant feature of the back surface is of particular importance, because moistening of the back surfaces of finishing papers has become customary in the trade as a pliability accentuating measure. In the absence of any water-resistant characteristics imparted by protective coating treatment, even slight wetting of the back surface tends to reduce the life of the abrasive paper in use, either by reason of deterioration of the backing by sending, or by reason of destruction of the glue bond through absorption of the moisture into and through the paper.

Thus a conventional untreated glue adhesive, the flexibility and toughness of which are unsurpassed as a making coat for finished paper,

are retained in my product. Even so, however,

the back surface of the treated backing has a water resistance which permits moistening thereof in accordance with the usual trade practice, without danger of reducing the life of the paper in use.

The versatility of the treated backing is to be found in its ability to receive with equal success as a substitute for a glue or other water: soluble adhesive making coat, other types of water-insoluble adhesive making coats, applied by other than aqueous solvents. While being miscible with glue and water-wettable, the underlying coat of diethylene glycol diabietate is also compatible with resinous, oil-modified resinous, and nitro-cellulose coatings of the type which are used in the manufacture of so-called waterproof papers, and are described in the literature and known as suitable for this purpose. Further, the underlying coat of my mate,- rial is wettable by hydrocarbon and other nonaqueous solvents, which are used for applying such waterproofing compounds.

For the above reason likewise, even when the glue making coat is retained, the back surface of the coated backing may be provided with a further coat of a water-resistant material or of a waterproofing material chosen for its com-' geous in its application to paper stock, it will be recognized that it will find uses in the treatment of cloth and other sheet material backings of the type used in the preparation of flexible abrasive sheet materials,

I claim:

1. A flexible abrasive sheet comprising a flexible backing of water-absorbent sheet material, a coating consisting essentially of diethylene glycol diabietate applied to said backing, a layer of an abrasive grit-binding adhesive applied to one surface of said coated backing, and abrasive grit embedded in said adhesive layer and bonded to the backing thereby.

2. A flexible abrasive sheet comprising a flexible backing of water-absorbent sheet material, a coating consisting of substantially unmodified diethylene glycol diabietate applied to said backing in a volatile solvent, a layer of an abrasive grit-binding adhesive applied directly over said coating, and abrasive grit embedded in said adhesive layer and bonded to the backing thereby.

3. A flexible abrasive sheet comprising a flexible backing of water-absorbent sheet material, a coating consisting essentially of diethylene glycol diabietate applied to said backing, a layer of a water-soluble adhesive applied over said coated backing, and abrasive grit embedded in said adhesive layer and bonded to the backing thereby.

4. A flexible abrasive sheet comprising a flexible backing of water-absorbent-sheet material, a coating consisting essentially of diethylene glycol diabietate applied to said backing, a layer of a water-soluble adhesive applied over said coated backing, abrasive grit embedded in said adhesive layer and bonded to the backing thereby, and a coat of a Water-insoluble, water-resistant material applled to the surface of said coated backing opposite the grit-bearing surface thereof.

5. A flexible abrasive sheet comprising a flexible backing of water-absorbent sheet material, a coating consisting essentially of diethylene glycol diabietate applied to said backing, a layer of glue applied over said coated backing, and abrasive grit embedded in said glue layer and bonded to the backing thereby.

6. A flexible abrasive sheet comprising a flexible paper backing, a coating consisting essentially of diethylene glycol diabietate applied to said backing, a layer of an abrasive grit-binding adhesive applied to one surface of said coated backing, and abrasive grit embedded in said ad-' hesive layer and bonded to the backing thereby.

7. A flexible abrasive sheet comprising a flexible paper backing containing not less than alpha cellulose content, a coating consisting essentially of diethylene glycol diabietate applied to said backing, a layer of an abrasive grit-binding adhesive applied to one surface of said coated backing, and abrasive grit embedded in said 0 adhesive layer and bonded to the backing 

